Antagonism by ?-aminobutyric acid of the stimulant effect of angiotensin II on cardiac sympathetic ganglia in spinal dogs

Publisher Website
Google Scholar
Abstract
The effects of angiotensin II and neuro-aminoacids administered through the right subclavian artery (i. a.) to the cardiac sympathetic ganglia were investigated in spinal dogs. Angiotensin II (1–8 μg) elicited a dose-dependent positive chronotropic effect which was reduced after i. a. injection of saralasin (100μg). The effect of angiotensin II was not reduced after combined treatment with either hexamethonium (10 mg/kg) plus atropine (0.1 mg/kg) or hemicholinium-3 (5 mg/kg) plus preganglionic stimulation. The dosedependent response to angiotensin II of heart rate was inhibited by GABA (50, 500μg), GABOB (500μg) and muscimol (50, 100μg). The inhibition of the response to angiotensin II by a small dose of GABA (50μg), but not by a high one (500μg), was antagonized by i. a. injection of picrotoxin (2 mg). The positive chronotropism induced by bethanechol (25, 50μg) and a small dose of acetylcholine (25μg) were significantly inhibited by a high dose (500μg) but not by a low dose (50μg) of GABA. These results confirm that angiotensin II stimulates cardiac chronotropism by acting on the angiotensin II receptor located at the cardiac ganglia and show that this stimulant effect is antagonized by GABA.